When I rehabbed my 18sf last winter I installed a dedicated starting battery and a dedicated "house" battery (electronics etc).
I tied them together with this kit from Blue Sea:
http://www.bluesea.com/products/7649...tery_Kit_-_65A
A single on off switch that independently switches each battery on and off and an automatic charging relay to keep them both topped off while also keeping them isolated from each other.
Worked flawlessly all summer.
You could even throw an emergency parallel in there if you wanted some backup starting capability.
